There are many practical applications involving a wireless network where it is desirable to have the lowest connection latency possible. Connection Latency is defined as the time taken for the transport of data from one device to another. One example of where low connection latency is required is within a gaming context where a handheld controller is wirelessly connected to a main console unit. Such applications typically require an overall latency of the wireless connection to be 5 ms or less. If the latency is greater, the user may notice the delay between pressing a command button on the controller and the response within the game. Another example where low latency is important is a virtual reality (VR) system with a wirelessly connected VR headset. Typically, game console and VR system providers use specialised firmware, hardware and/or software for establishing a low latency connection.
One popular protocol for wireless connectivity is Bluetooth. A recent version of this is the Bluetooth Low Energy (BLE) standard, also referred to as Bluetooth Smart. Its operation is defined by various standards and specifications which are managed by the Bluetooth Special Interest Group. Given the ubiquitous nature of Bluetooth connectivity, it is desirable that low latency connection can be established using the Bluetooth or BLE protocol.
However, the BLE specification defines a connection model for BLE with a minimum connection interval of 7.5 ms. The purpose of this minimum connection interval is to save power, which is a key objective of the BLE standard. The advantage of having a relatively long connection interval is that significant power is saved, since a device can sleep most of the time between connection events. The disadvantage is that if a device has data that it needs to send, it must wait until the next connection event. A shorter connection interval provides more opportunity for data to be sent or received, as the two devices will connect more frequently.
Under the BLE standard (low power method), and using the minimum connection interval, two devices cannot connect and exchange data more frequently than every 7.5 ms. For a high power solution, the BLE specification defines a method that enables both connected devices to continue sending and receiving (using the More Data bit) but this is not practical for a battery operated handheld device. For applications such as gaming, the amount of data that needs to be sent (the payload) is typically small, such as a handheld controller transmitting data representing the pressing of a command button or movement of the VR handheld unit.
The BLE standard defines two device roles at the Link Layer for a connection: the master device and the slave device. These are the devices that act as initiator and advertiser respectively during creation of the connection. A master device can manage multiple simultaneous connections with different slave devices, whereas each slave device can only be connected to one master device. Thus, a network can be formed which comprises a master device and multiple slave devices, and this is called a piconet.
Within the network, each slave device has its own unique media access control address (MAC address). This is a device identifier assigned to network interfaces for communications at the data link layer of a network segment. It is possible to change the MAC address on most modern hardware and many network interfaces (including wireless ones) support changing their MAC address.